The testing of manufactured devices at the end of the manufacturing process or of subassemblies at subassembly and subprocess points in the manufacturing process are well known. An example of a test module for a plurality of magnetic disk drives is shown in U.S. Pat. No. 4,888,549, assigned to Wilson Laboratories, Inc. The use of automated testers or computers to conduct the testing and to accumulate the test results is also known. An example of an automated tester computer is illustrated in U.S. Pat. No. 4,841,456.
Such testers typically test each device and pass or fail the device for the specific test. If the test failure is repairable, the device is reworked, reinserted in the manufacturing line, and retested. The test data is often accumulated and may be reviewed in batch mode. The typical assembly line is singular and the test data accumulated in a tester may be utilized to analyze the specific associated assembly line.
Magnetic disk files, however, are currently assembled from components, where not only do different components arrive from different sources, but the same components, such as disks, are provided from different sources. Further, some of the assembly may be done in an assembly line fashion, but most often, the assembly is done in subassemblies at ones of many parallel stations, the output of the parallel stations stored together or intermixed between sequential stations, and the intermixed subassemblies separated into non-segregated groups for further assembly or testing. Hereinafter, the intermixing and subsequent separation into non-segregated groups is called a "variegated" process stream. The reason for the variegated process is because the steps require substantially different lengths of time to accomplish. Thus, more stations are required to accomplish the longer process steps. Only with a variegated process stream, can the overall manufacturing process flow smoothly. Thus, there is no direct correlation between the tester and the source of the components or the preceding assembly stations for the devices being tested.
At some point, the accumulated testing data may be utilized in batch mode to analyze the assembly process. A key problem is the need to ascertain a common tester, tool, station, source of components or process that produced the failing devices.
A typically expensive subsequent analysis of accumulated testing data by failure analysis personnel might lead eventually to an understanding of a root cause source of a problem. What is needed is a means and process for identifying the source of the problem during the manufacturing process on a real time basis, so that the problem may be addressed and corrected before productivity or production will be lost, or excess scrap or rework is created.